Automatic control system for controlling moving craft



Nov. 25, 1952 F. w. MERz-:DlTH

AUTOMATIC CONTROL SYSTEM FOR CONTROLLING MOVING CRAFT Filed July e, 19474' Sheets-Sheet l Nov. 25, 1952 F. w. MEREDITH 2,619,523

AUTOMATIC CONTROL SYSTEM FOR OOMTROLLTMG MOVING CRAFT Filed July 8, 19474 Sheets-Sheet 2 INveN rag Nov. 25, 1952 F. w. MEREDITH 2,619,523

AUTOMATIC CONTROL SYSTEM FOR OONTROLLTNG MOvTNG CRAFT Filed July 8, 19474 Sheets-Sheet 3 d CLUTCH T nloglo j? 52 sz @o 11N-vc NTO@ Nov. 25, 1952F. w. MEREDITH AUTOMATIC CONTROL. SYSTEM FOR CONTROLLING MOVING CRAFT 4Sheets-Sheet 4 Filed July 8, 1947 ab Mmm! mu v nu@ an. if Li T112@ il0MM Q, M fwaluw Patented Nov. 25, 1952 AUTOMATIC CONTROL SYSTEM FOR CON-TROLLING MOVING CRAFT Frederick William Meredith, Cricklewood, London,England, assignor to S. Smith & Sons (England) Limited, London, England,a British Company Application July 8, 1947, Serial No. 759,625 In GreatBritain June Z0, 1946 Section 1, Public Law 690, August 8, 1946 Patentexpires June 20, 1966 (Cl. S18- 489) Claims.

This invention relates to automatic control systems for controllingmoving craft both air and marine about a control axis.

It is usual to control an aircraft about three axes, pitch, roll andyaw, and a marine craft about one, yaw. Furthermore it is known toeffect such control by providing a deviation detector to detect a changein attitude of the craft about a control axis from a datum attitude andto operate a valve or a switch controlling a servomotor which operatesthe appropriate control surface to stabilise the craft and return it tothe datum attitude in pitch, roll or yaw as the case may be. In thisknown arrangement the valve or switch is generally in two parts, onebeing operated by the detector and the other being mechanically coupledto the servomotor so that the servomotor is operated in accordance withthe misalignment between the detector and the servomotor.

With an automatic control system of this type the usual way to changethe datum attitude is to displace one of these two parts of the valve orswitch in relation to its operating member by an amount corresponding tothe desired change of attitude t0 create a false misalignment, so thatthe craft changes its attitude until the parts are restored to theirinitial position.

The object of the present invention is to provide an automatic controlsystem which does not make use of the above mentioned misalignmentsignal to effect stabilisation (although the misalignment may be used toeffect monitoring) and in which nevertheless provision is made foreffecting a change of attitude. A further object of the invention is tointroduce damping without interfering with any desired change ofattitude.

An automatic control system for controlling a moving craft, according tothe present invention, comprises a device for measuring rate of turnabout a control axis of the craft, means for controlling the attitude ofthe craft about that axis in accordance with the measured rate of turnto maintain a predetermined attitude and means for effecting a change ofattitude at a predetermined rate.

The means for controlilng the attitude of the craft preferably comprisesa servomotor operating the appropriate control surface and arranged tooperate at a speed proportional to the measured rate of turn.

The means for effecting a change of attitude may comprise means forrotating the device relatively to the aircraft about the said axis.Alternatively where the device generates an E. M. F.

proportional to the rate of turn the means for effecting a change ofattitude may comprise means for injecting a counter-E. M. F. into thesystem, whereby the craft changes its attitude at a rate proportional tothe injected E. M. F. In this latter arrangement damping may be effectedby introducing into the system a further E. M. F. proportional to thedifferential with respect to time of the magnitude of the differencebetween the E. M. F. generated by the said device and the said injectedE. M. F. so that the further or damping E. M. F. only becomes effectiveupon departure of the rate of turn from the predetermined rate of turn.It should be noted that if only the E. M. F. generated by the saiddevice is differentiated the damping E. M. F. would delay the initiationof the turn to effect a change of attitude.

The invention will now be described by way of example with reference tothe accompanying drawings, of which:

Figure l illustrates diagrammatically the layout of an automatic controlsystem for controlling an aircraft about all three axes;

Figure 2 illustrates in further detail the rateof -turn instrumentsshown in Figure 1;

Figure 3 illustrates in further detail the pendulums shown in Figure l;

Figure 4 illustrates in further detail the tangent potentiometer shownin Figure l;

Figure 5 illustrates in further detail the control circuits shown inFigure l, and

Figure 6 is a diagram of a valve circuit for adding in the differentialof the signal in an A. C. signal circuit.

As disclosed in my copending application S. N. 655,684 filed March 20,1946, an aircraft can be stabilized by three rate-of-turn gyroscopes; inyaw by gyroscope I controlling rudder 2, in roll by gyroscope 5controlling ailerons 6 and in pitch by gyroscope 8 controlling elevators9. A compass controlled directional gyroscope 3 monitors course duringstraight flight, pendulum 'I monitors bank and pitch pendulum I 0monitors pitch. Ring I3 pivoted about roll axis I4 gimbals platform IIabout pitch axis I2. Adjustment is made by motors I5 and I6. Hysteresismotors I9, coupled to their respective control surfaces by clutch I1 andgear box I 8, have one phase connected to a reference source 20 and theother phase to a control amplifier 2I and a hysteresis generator 22.Contacts 23 shunt bank pendulum 1 on turns. Tangent potentiometer 24gives a signal 0f movement of platform II in roll. Pendulum 25 detectsside-slip. Selsyn transmitters 2t and 23 are supplied by source 133 ofthe same frequency as source 2S and are connected to Selsyn receivers 21and 29, respectively, which are associated by relays 3u, 3i and brakemember 32. Relay 3l controls contacts 33 to introduce side-slip signalfrom pendulum 25 into the circuit.

A suitable rate-of-turn gyroscope for use as gyroscope l, 5 or 8 isillustrated diagrammatically in Figure 2. As there shown a gyroscopecomprises a rotor tl mounted on spin axis in a gimbal ring 36 gimbaledabout an axis 3l on a xed base 38. Carried by the gimbal ring 35 is apotentiometer contact 39 arranged to sweep across a xed arcuatepotentiometer resistance il as the ring rotates relatively to the baseabout the axis 31. The ring 36 is restrained by a spring 4i to a centralposition in which the contact 39 engages the mid point ft2 of theresistance Gil. The resistance il@ is connected across the A. C. source@3. The electrical output of the gyroscope appears between the contact39 and the mid point 62.

In operation any turn about an axis normal to the base 3S results inprecession of the gyroscope about the axis 37 against the springrestraint t0 an extent determined by the rate of turn. Hence the outputvoltage will be proportional to the rate of turn.

It will be appreciated that the rate-of-turn gyroscope described abovemay be arranged to measure rate o turn about any of the three aircraftaxes and that the three gyroscopes may readily be made interchangeable.

As an alternative to the use of gyroscopes in the arrangement describedwith reference to Figure l, the rate-of-turn devices described in UnitedStates patent application No. 504,072 may be used.

Pendulums i, it and 25 may be constructed as shown in Fig. 3. Pendulumarm ifi traverses arcuate resistance i5 supplied by source 43. Thesignal is taken from conducting arm it and the central tap s ofresistance t5. Tangent potentiometer 2li shown in Fig. 4 comprises aconducting arm il which traverses linear resistance d3 supplied bysource llt, The signal is taken from arm di and central tap il@ ofresistance 4t.

Control is effected by turn control lever 5S and pitch control lever El.Lever 5S, pivoted at 8i carries insulated contact strip 52 over arcuatepotentiometer resistance 53 and also insulated Contact strip 5d inpermanent contact with segment 55 and if displaced left, over segment 55or right, over segment 5i. Ring 3 drives contact arm 5s over resistance59. D. C. motor IS has eld winding @il connected between strip 52 andarm 58.

Lever 5l pivoted at 6i carries strip @2 over resistance t3. Field Sd ofD. C. motor I5 is connected across battery 55. Switch 65 operated bycoil 67 and buttons GS and 69 cuts automatic control in or out.. In thedeenergized position shown one brush of motor l5 is connected topendulum l@ through contacts l@ and lead ii. Pendulum it may engageeither lead 'i2 or i3 to the terminals of battery 65. Contacts i4 and'E5 are closed in response to pressing button d3 to place the automaticcontrol in operation.

The arrangement described above is modied to introduce damping into therudder control circuit by adding to the other voltages applied to theinput of the amplifier 2l a damping voltage proportional tothedifferential of the algebraio sum of the voltages derived from therate lated lGG- voltages derived from the rate of yaw gyroscope l andthe potentiometer 2d is applied to the input of the circuit shown inFigure 6.

As there shown two triodes V1 and V2, which may conveniently be in oneenvelope, are circulated so that the modulated 4G0- A. C. signal isapplied differentially to the two grids through the input transformerlill.

A. C. voltage of the reference frequency (400-) and phase is applied inthe same phase (push-push) to the two anodes by secondary windings ft2and its on an anode transformer, the primary of which is connected to asuitable voltage source.

The half wave anode pulses are applied through condensers ltd and H tothe opposite ends of the primary winding of an output transformer itsthe centre tap of this primary winding being connected by a lead l0?,which carries the A. C. components of the two valve currents, to theadjustable tap on a cathode balancing resistor H38, the ends of whichare connected to the two cathodes of the valves V1 and V2.

The direct current components of the two valve currents are led throughleads its and H9 to opposite ends of a grid biassing network to whichthe grids are connected by grid leak resistors Hi and i l2, the inputcircuit being isolated by condensers l i3 and l lli.

rlhe grid leali iii is connected through a resistance R1 direct to thelead it and, through a condenser C1 to a tapping l l5 on a resistance Iit which in series with a resistance H8 joins lead lli! to lead It).

Similarly the grid leak l i 2 is connected through a resistance R2 tolead Hil and, through a condenser C2 to a tapping lil on resistance iIS.

The nodal point of the two resistances H and H8 is joined by a line H9to the tapping on the cathode balancing resistance li. This line carriesthe entire D. C. component of the two valve currents and mayconveniently pass through a source of D. C. potential to offset thenegative grid bias produced by the resistance les and the resistancesIli and HS.

A variable resistance itt is connected across the two tappings l i5 andl il whereby the amount of transient regenerative differential-biasapplied to the grids may be adjusted.

The output transformer secondary feeds a potentiometer iti and is tunedby the condenser H22. By these means the overall gain factor of thecircuit can be adjusted to the required value. The A. C. load in theanode cathode circuits is purely resistive so that the voltage acrossthe output potentiometer mi is in phase with the valve pulses andtherefore with the reference voltage applied to the anode transformer.

The two condensers C1 and C2 are of equal values as are the tworesistances R1 and R2.

The circuit operates as follows:

As lonCr as the input signal to transformer itl isr zero and the twogrids are equally biassed, balanced half wave pulses are applied to theoutput transformer It and the voltage across the output terminals isalso zero.

Again, as long as the two grids are equally biassed, any in phase signalapplied to the transformer it# will unbalance the anode pulses thusleading to an in phase signal at the reference frequency across theoutput potentiometer.

But diierential bias of the two grids will `also unbalance the anodepulses so that even in the absence of an input signal, an output signalwill appear proportional to the amount of differential bias applied tothe grids.

Let E1 be the A. C. signal applied to the input transformer,

E2 the output A. C. signal appearing across the tapping of thepotentiometer |2l, and

Eb the differential D. C. -bias applied to the grid leak returns.

Then E2=E1+7cEz1, the overall gain being so adjusted.

Let I1 and I2 specify the D. C. components of the two valve currents.

Then Ezofh-Iz (where OC is the proportionality sign) To simplify theanalysis it is assumed that R1 and Rz are large compared with thepotential dividers H6 and l I8 so that each of these carriessubstantially the Whole demodulated current of its respective valve.

It is assumed as obvious that the effect of varying the resistance |20is equivalent to varying simultaneously and symmetrically the twopotential tapping points H5 and ll'l on the potential dividers H5 andH8.

Then referring all D. C. potentials to the line lill the potentialapplied to the bottom of R2 is *Rall and the potential applied to thebottom of R1 is Rizla where Rs is the value of each of the resistancesH6 and I I8.

Again, from considerations of symmetry it may be stated and if Er1 isthe potential applied to the bottom of resistance R2 ET,=-Ram(I-l-I) andif Er2 is the potential applied to the return I Il of C ET.: *Rama-I)where m represents the adjustable potential ratio of the tappings I land l I1.

Then if E131 be the potential at the return of the grid leak l i2 whereD represents the differential operator and R and C are the values of R1and R2 and C1 and Cz respectively.

Thus, Writing t1 for RC, which has the dimensions of time.

But the diiferential bias Eb---Erel-EB2 so If g represents the mutualconductance of each of the valves and assuming that the function of theresistor IGS is merely to adjust the mutual conductances to equality andto swamp out accidental variations of the mutual conductances at theexpense of a resulting low value of g, it may be stated.

Since we have shown that EWI, writing E2. for b1 l-i-tlD-l-gjgRamtlDabgEl 2(1-I-1') l (l-mr) then Since the overall factor is adjustable toany required value the constant value by adjustment of m until mrapprroaches 1, when g? approaches 1+t1D The output E2 is thus applied tothe input of the amplifier 2l in the place of that previously derivedfrom the rate of yaw gyroscope l and the potentiometer 24.

I claim:

1. An automatic control system for controlling a moving craft comprisinga gimbaled platform mounting a device giving a first signal inaccordance with rate of turn of the craft about a control axis, anamplifier, a servomotor controlled by the output of said amplier andactuating a control surface controlling the craft about the said controlaxis, means giving a second signal in accordance with the rate ofmovement of said control surface, means to apply the rst and secondsignals in opposition to the input of the amplifier to cause the controlsurface to be actuated at a rate substantially proportional to the rateof turn of the craft about the control axis to stabilise the craft aboutsaid axis, and means connected to said platform to rotate said platformand to change the course of the craft. about said axis at a.predetermined rate.

2.` An automatic control system for controlling a, moving craftcomprising a gimbaled platform having thereon a, device giving a firstsignal in accordance with rate of turn of the craft about a controlaxis, an amplifier, a servomotor controlled by the output of saidamplifier and actuating a control surface controlling the craft aboutsaid control axis, means giving a second signal in accordance with therate of movement of said control surface, means to apply the first andsecond signals in opposition to the input of the amplifier to cause thecontrol surface to be actuated at a rate substantially proportional tothe rate of turn of the craft about the control axis to stabilise thecraft about said control axis and means connected to said platform torotate said platform and the rate of turn device about the control axisrelative. to the craft at a predetermined rate to cause the craft torotate about the control axis in the opposite direction to that of therotation of said rate of turn device and at the predetermined rate insuch a manner that the control surface operates to rotate the craft at arate equal and opposite to that at which said platform is rotatedwhereby said platform Will be level in space when its rotation ceasesand the craft Will have been turned through the angle through which theplatform rotated.

3. An automatic control system for controlling a moving craft comprisinga -gimbaled rotatable platform mounting a device giving av rst signal inaccordance with the rate of turn of the craft about a control axis, anamplifier, a servomotor controlled by the output of said amplifier andactuating a control surface controlling the craft about said controlaxis, means giving a second signal in accordance with the rate ofmovement of said control surface, means to apply the first and secondsignals in opposition to the input of the amplifier' to cause thecontrol surface to be actuated at a rate substantially proportional tothe rate of turn of the craft about the control axis to stabilise thecraft about said axis and means to inject a third signal into theamplifier input equal and opposite to the said first signal When thecraft is turning about the control axis at a predetermined rate to causethe craft to turn about the said control axis at the said predeterminedrate in such a manner that the control surface operates to rotate thecraft at a rate equal and opposite to that at which said platform isrotated whereby said platform Will be Y level in space when its rotationceases and the craft will' have turned through the same angle as theplatform.

4. An automatic control system for controlling a moving craft comprisinga devi-ce giving aA rst electric signal in accordance with rate of turnof the craft about a control axis an electric amplier, a servomotorcontrolled by the output of said amplifier and actuating a controlsurface controlling the craft about said Ycontrol axis, a tachometricelectric sig-nal generator giving a second signal in accordance with therate of movement of saidv control surface, means to apply theY first andsecond signals in opposition to the input of the amplier to cause thecontrol surface'to be actuated at a rate substan- Y tially proportionalto the rate of turn of the craft about the control axis tov stabilisethe craft about said axis and means to change the course of the craft byrotation of the craft about said axis at a predetermined rate.

5. An automatic control system for controlling a moving craft comprisinga device giving a rst electric signal in accordance with rate of turn ofthe craft about a control axis, an electric amplifier, a servomotorcontrolled by the output of said amplier and actuating a control surfacecontrolling the craft about said control axis, a tachometric electricsignal generator giving a second electric signal in accordance with therate of movement of said controlsurfaceL means to apply the rst andsecond signals in opposition to the input of the amplifier to cause thecontrol surface to be actuated at aratefsubstantially proportional tothe rate of turn of the craft about the control axis to stabilise` thecraft about said axis and means to rotate the rate of turn devicerelative to the aircraft about the control axis at a predetermined rateto cause Y the aircraft to turn about the said control axis in theopposite direction atA the same predetermined rate.

6. An automatic control system for controlling a moving craft comprisinga device giving a first electric signal in accordance with rate of' turnof the craft about a control axis, an electric amplifier, a servomotorcontrolled by the output of said amplifier and actuating a controlsurface controlling the craft about said control axis, a tachometricelectric signal generator giving a second electric signal in accordancewith the rate of movement of said control surface, means to apply therst and second signals in opposition to the input of the amplifier tocause the control Surface to be actuated at a rate substantiallyproportional to the rate of turn of the craft about the control axis tostabilise the craft about said axis, and means to inject a thirdelectric signal into the amplier input equal and opposite to the said'first signal when the craft is turning about the control axis at apredetermined rate to cause the craft to turn about the said controlaxis at the said predetermined rate.

7. An automatic control system' for controlling a moving craftcomprising a device giving a first electric signal in accordance withrate of turn of the'craft about a control axis, an electric amplifier, aservomotor controlled by the output of said amplier and actuating acontrol surface controlling the craft about said control axis, atachometric electric signalV generator giving a second electric signalin accordance. with the rate of movement of the control surface, meansto apply the first and second electric signals in opposition to theinput of the amplifier to cause the control surface to be actuated at arate substantially proportional tothe rate of turnof the craft about thecontrol axis tostabilise the craft about said axis, means to inject athird electric signal into the amplifier input equal and opposite to thesaid first signal when the craft is turning about the control axis at apredetermined rate to cause the craft to turn about the said controlaxis at the said predetermined rate, means to` generate a fourthelectric signal in accordance with the rate of change with respect totime of the difference between the aforesaid nrst and third signals andmeans to apply the said fourth signal to the amplifier input to improvethe damping of the system.

8. An automatic control system according to claim 7 wherein the means togenerate the fourth electric signal comprise a further amplifier to theinput of which is applied the difference between the first and thirdsignals together with a part of the further amplifier output, fed backdegeneratively through an integrating circuit to the input of saidfurther amplifier.

9. An automatic control system according to claim '7 wherein the meansto generate the fourth electric signal comprise a pair ofgrid-controlled amplifier valves to the control grids of which thedifference between the first and third signals is applied in push-pulland similar integrating circuits are connected between anode and grid ofeach valve to feed back the integral of the output of each valvedegeneratively to the input.

10. An automatic control system according to claim '7 wherein thesignals are amplitude-.modulated A. fC. signals and the means togenerate the fourth electric signal comprise a pair of gridcontrolledamplifier valves to the control grids of which the difference betweenthe rst and third signals is applied in push-pull and there are appliedrespectively to the anodes of the valves two A. C. voltages in phase andof equal amplitude, said voltages being in phase with the voltage on thegrid of one valve and in anti-phase with that on the other, whereby thevalves pass pulses of direct current and the difference between thedirect currents through the valves is in accordance with the inputsignal, two similar resistors and two similar condensers, one resistorbeing connected between anode and grid of each valve and one condenserbeing connected between grid and cathode of each valve to feed-backdegeneratvely to each grid a direct voltage in accordance with theintegral of the current through the valve and a transformer whoseprimary is connected between the anodes of the two valves and acrosswhose secondary is developed the fourth signal, said fourth signal beingan A. C. signal substantially in accordance with the rate of change ofthe difference of the first and third signals.

11. In combination an automatic control system for controlling a movablecraft comprising a device for generating an electromotive forceproportional to the rate of turn about a control axis of the craft,means for controlling the attitude of the craft about said axis inaccordance with said electromotive force to maintain a predeterminedattitude, means for injectingl a counterelectromotive force into thesaid system to effect change of attitude at a rate proportional to theinjected counterelectromotive force and means for introducing into thesystem a third electromotive force for damping the system proportionalto the differential with respect to time of the electromotive forcegenerated by said device and the said injected counterelectromotiveforce so that third or damping electromotive force only becomeseffective upon departure of the rate of turn from the predetermined rateof turn, said means for introducing said third electromotive forcecomprising an amplifier, means for apply- 10 ing to the input of saidamplier the electronictive force generated by said device and the saidinjected counterelectromotive force and means for feeding a part of theamplified output through an integrating circuit back to the inputdegeneratively.

12. An automatic control system as claimed in claim 11 wherein the meansfor introducing the said damping E. M. F. into the circuit comprises twogrid controlled valves to the control grids of which the alegbraic sumof the input E. M. F.s is applied in push-pull and feed back pathsconnecting the anode of each valve to the control grid of the same valvethrough an integrating circuit.

13. 'An automatic control system as claimed in claim l2 wherein the saidfeed back paths comprise means for generating a voltage proportional tothe difference in the currents flowing through the valves, means forapplying said voltage to an integrating circuit and means for applyingthe voltage resulting from such integration differentially to the gridsof said valves.

14. An automatic control system as claimed in claim 13 in which the saidE. M. F.s are A. C. at a reference frequency and in which the saidamplifier comprises two grid-controlled valves to the grids of which theinput E. M. F.s are applied in push-pull and to the anodes of which anA. C. voltage of reference frequency is applied in push-push, a firstresistance connecting the anode circuit to the control grid of one ofthe valves, a second resistance connecting the anode circuit to thecathode of one of the valves, similar resistances connecting the anodecircuit to the control grid and cathode of the other valve, and twocondensers each of which is connected between a tapping point on thefirst resistance of one of the valves and a tapping point on the secondresistance of the other valve.

15. An automatic control system as claimed in claim 11 in which the saidE. M. F.s are A. C. at a reference frequency and are applied in pushpull through coupling condensers to two control grids of a pair ofvalves which are independently forced to pulse in push-push at thereference frequency, means of separating the direct current andalternating components of the anode pulses, means of applying thealternating components in push-pull to the means for controlling theattitude of the craft, means for applying differential bias to thecontrol grids and means for controlling said differential biasdegeneratively with delay in accordance with the difference of thedirect current components of the two valves.

FREDERICK WILLIAM MEREDITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,703,280 Minorski Feb. 26, 19292,401,168 Kronenberger May 28, 1946 2,415,430 Frische et al Feb. 11,1947 2,415,819 Halpert et al Feb. 18, 1947

